It is desirable to validate corona free operation of electrical equipment, operating in a reduced pressure environment, using non-invasive detection techniques. Radio frequency (RF) corona detection methods are sometimes effective for such validation, but test results vary due to field strength. Furthermore, testing of electrical equipment such as electrical power converters with properly designed electro-magnetic interference (EMI) filters and shielded enclosures further mask test results and attenuate signal strength, thus not allowing an accurate prediction of partial corona discharge onset.
A Rogowski coil may serve as a current sensor that develops an electrical output potential that is proportional to the rate of change of electrical current in the circuit that it measures. One advantage of a Rogowski coil over other types of current transformers usable as current sensing devices is that it may have an open-ended and flexible construction, and therefore it may wrap around a live conductor without disturbing it.
Since a Rogowski coil has an air core rather than an iron core, it has a low inductance and can respond to fast-changing currents. In addition, because it has no iron core to saturate, it is highly linear even when subjected to large currents, such as those used in electric power transmission, welding, or pulsed power applications. A correctly constructed Rogowski coil, with equally spaced windings, is largely immune to electromagnetic interference. Furthermore, since this type of coil has an output that increases with rate of sensed current change, its response increases at higher frequencies.
Until now, application of a Rogowski coil for on-line detection of partial corona discharge has been through the ground line of power equipment, and the Rogowski coil may sense the pulse current due to such discharge from the ground line by way of computer analysis. However, the frequencies of such current signals may range up to tens of mHz, and thus computer testing equipment capable of such analysis may be extremely costly. Furthermore, grounding is a complicated issue and other signals in the ground line may mask the partial corona discharge signals.